Autologous and allogeneic bone marrow transplantation are widely used for treatment of a number of hematologic malignancies, including aggressive non-Hodgkin's lymphomas. However, relatively small numbers of patients with low grade lymphoma or chronic lymphocytic leukemia have been treated using this approach. There is reluctance to perform potentially lethal treatment procedures for diseases with relatively long natural histories that tend to occur in more elderly patients. Although these diseases are characterized by initial chemotherapy responsiveness, many of these patients are heavily pretreated and have acquired chemotherapy resistance and decreased marrow reserve by the time of consideration of bone marrow transplantation as a treatment option. The very high incidence of bone marrow infiltration in these diseases has made it difficult to use autologous stem cells for rescue after high dose myeloablative therapy. However, because these diseases are incurable using conventional therapy, there has been increased interest recently in the use of high dose ablative therapy and stem cell support. Studies have focused on the timing of such procedures (either early in the treatment course before chemoresistance develops or after subsequent relapse), the source of stem cells, and whether purging of malignant cells from autologous stem cells is required.